Method and device for recognition of a collision with a pedestrian

ABSTRACT

A method of deciding with a high reliability whether an impact with the front side of a vehicle has been caused by a pedestrian is described. Two decision criteria are formed, and only if both decision criteria are met is it decided an impact with a pedestrian has occurred. The first decision criterion is determined by the fact that the pressures or deformations measured by a sensor on the bumper and a sensor in the area of the front edge of the engine hood are compared with reference quantities typical of impact with a pedestrian. The second decision criterion is determined by the fact that the changes in velocity and/or acceleration of the vehicle caused by an impact are determined, and then the changes in velocity and/or acceleration are compared with reference quantities which are typical of impact with a pedestrian.

FIELD OF THE INVENTION

[0001] The present invention relates to a method and a device fordetecting the impact of a pedestrian with a vehicle, at least one sensorbeing provided on the bumper and at least one sensor in the area of thefront edge of the hood of the engine to measure the pressures ordeformations caused by impact and to form a first criterion for thedecision as to whether there has been an impact with a pedestrian on thebasis of the sensor output signals by comparison with referencequantities.

BACKGROUND INFORMATION

[0002] A method of detecting an impact of a pedestrian with a passengervehicle is discussed in PCT Publication No. WO 97/18108. To protect thepedestrian from serious injuries in the event of an impact of apedestrian with the front side of a vehicle, one or more airbags may beprovided on the engine hood or on the windshield for deployment in theevent of an impact with a pedestrian. Another safety measure for animpact with a pedestrian is for the engine hood to be inclined at anangle to catch the pedestrian. Deployment of such safety devices maydepend upon the impact with a pedestrian being detected reliably andalso being differentiated unambiguously from impacts with other objects.The related art discusses utilizing for detection of a pedestrian impactthe basic kinematics of a pedestrian on impact with the front side of apassenger vehicle. As a rule, the first point of contact of a pedestrianwith a vehicle is the bumper. Therefore, a first sensor which respondsto the acting force or the deformation may be located on the bumper ofthe vehicle. Through contact with the bumper, the pedestrian may receivea rotational momentum which throws him onto the engine hood. In otherwords, impact with the bumper may be followed after a time lag byanother impact with the engine hood. Therefore, a second sensor whichresponds to pressure or deformation may be situated on the front edge ofthe engine hood. The sensor output signals may be compared withreference quantities that are representative for impacts with apedestrian. If they match or if there is a correspondence within acertain range of tolerance between the sensor output signals and thereference quantities, it may be decided that this is due to an impactwith a pedestrian. As a result of this decision, the available safetydevices may therefore be deployed.

[0003] [The] An object of the present invention is to provide a methodand a device with which it is possible in the event of an impact on thefront side of a vehicle to decide with the highest possible reliabilitywhether this impact has been caused by a pedestrian.

SUMMARY OF THE INVENTION

[0004] An exemplary embodiment of the invention involves at least onesensor mounted on the bumper and at least one sensor in the area of thefront edge of the engine hood to measure the pressures or deformationscaused by an impact. In the exemplary embodiment, the sensor outputsignals are compared with reference quantities to derive a firstcriterion for the decision as to whether it is a pedestrian impact, andthe change in velocity and/or acceleration of the vehicle caused by theimpact may be determined. By comparing the change in velocity and/oracceleration with a reference quantity, a second criterion for decidingwhether it is a pedestrian impact may be formed, and when both decisioncriteria are met, the decision may be made that it is a pedestrianimpact.

[0005] In addition to the first known decision criterion, anotherdecision criterion may be formed from the change in velocity and/oracceleration of the vehicle because of an impact, and the decision for apedestrian impact may be made on the basis of the two decision criteria.Therefore, a high reliability may be achieved in detecting an actualimpact with a pedestrian.

[0006] In deriving the second decision criterion, it may be expedient totake into account braking which is initiated before an impact, becausethis has an effect on the change in velocity and/or acceleration of thevehicle caused by an impact. In the case of braking initiated before animpact, the second decision criterion may be derived from the change inacceleration alone because in the case of brake-locked wheels, thevelocity sensors present in the vehicle will yield a value of 0. Thus,in this situation, no change in velocity may be determined by comparisonof the velocities before and after an impact. The situation may bedifferent with an acceleration measurement, which may be performedindependently of movement of the wheels of the vehicle.

[0007] Reference quantities for the sensor output signals may include,for example, signal amplitudes typical of a pedestrian impact. Thereference quantity used could also be the signal sequence of sensoroutput signals over time typical of an impact with a pedestrian.

[0008] Pressure and deformation sensors based on different measurementprinciples may also be used. These may include sensors made of wirestrain gauges or piezo films or sensors utilizing the anisotropicmagnetoresistive effect or the Hall effect. It also may be possible touse sensors having a pressure-dependent light transmissioncharacteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 shows a front view of a motor vehicle having two sensors.

[0010]FIG. 2 shows a block diagram of a device for detecting an impactwith a pedestrian.

[0011]FIG. 3 shows curves of sensor output signals in an impact with apedestrian.

[0012]FIG. 4 shows a flow chart of the method for detecting an impactwith a pedestrian.

DETAILED DESCRIPTION

[0013] In an exemplary embodiment for detecting with the highestpossible certainty whether a given impact with the front side of avehicle is a pedestrian impact, vehicle 1 is equipped with a firstsensor 3 on its bumper 2, as shown in FIG. 1, and a second sensor 5 onthe front edge of its engine hood 4. Both sensors 3 and 5 may bepressure sensors or deformation sensors. Therefore, sensors 3, 5 may bemounted on bumper 2 as well as on the front edge of engine hood 4because it may then be possible to detect the characteristic kinematicsof a pedestrian impact with vehicle 1. In other words, if a vehiclestrikes a pedestrian at its front side, the pedestrian may first come incontact with the bumper, so that sensor 3 on bumper 2 delivers a signalwhich depends on pressure or deformation. Bumper 2 absorbs only a smallportion of the total kinetic impact energy. Contact with the bumper mayimpart to the pedestrian a rotational momentum, possibly throwing himonto the hood of the engine. Second sensor 5 on engine hood 4 may thendetect this pressure or deformation produced by the impact with thepedestrian.

[0014]FIG. 2 shows a block diagram of a device, and FIG. 4 shows a flowchart of a method, with which impact with a pedestrian may be detectedwith a high reliability. In FIG. 2, reference numbers 3 and 5 denotepressure and deformation sensors mounted on the bumper and on the enginehood of the vehicle.

[0015] When sensor 3 on bumper 2 and sensor 5 on engine hood 4 arementioned here, this also includes the possibility of multiple sensorsor sensor elements being present on both bumper 2 and engine hood 4.Sensors based on different principles for measurement of pressure anddeformation may be used. For example, the sensors may be wire straingauges or piezoresistive films. Optical sensors having apressure-dependent light transparency may also be used. Likewise,sensors based on the Hall effect or the anisotropic magnetoresistiveeffect may also be used. Any sensor which produces a pressure- ordeformation-dependent signal, regardless of the method, may be suitablein principle.

[0016] Output signals s1 and s2 of sensors 3 and 5 may be sent tocontrol unit 6. In addition, output signal v of velocity sensor 7,acceleration signal b of acceleration sensor 8, and brake signal brdelivered by brake system 9 may all be sent to control unit 6. Ifcontrol unit 6 decides on the basis of aforementioned input signals s1,s2, v, b, br that an impact with the front side of the vehicle has beenproduced by a pedestrian, then control unit 6 delivers deployment signala to safety device 10. Safety device 10 may be, for example, one or moreairbags arranged on the engine hood or on the frame of the windshield.The airbags may be adapted to inflate on impact with a pedestrian.Furthermore, to protect the pedestrian, engine hood 4 may be inclined atan angle by a spring mechanism or a pyrotechnic mechanism when controlunit 6 delivers deployment signal a.

[0017]FIG. 4 illustrates a method of detecting a pedestrian impact in aflow chart. Pressures and/or deformations s1 and s2 occurring on bumper2 and on engine hood 4 may be measured with sensors 3 and 5 in methodsteps 11 and 12. In addition, velocity v and acceleration b of thevehicle may be measured continuously according to method steps 13 and14. Brake signal br may also be determined according to method step 15.

[0018] In method step 16, sensor signals s1 and s2 are compared withreference quantities characteristic for a pedestrian impact. FIG. 3shows curves for both sensor signals s1 and s2 which may be typical of apedestrian impact. First, sensor 3 on bumper 2 of the vehicle deliversoutput signal s1 because, upon impact with a pedestrian, the pedestrianwill first come in contact with bumper 2. Output signal s2 of sensor 5on engine hood 4 follows with a time lag Δt which is typical of apedestrian impact. The amplitudes of output signals s1 and s2 of sensors3 and 5, as well as time lag Δt between two output signals s1 and s2,may be characteristic of a pedestrian impact. These characteristicquantities may be used in method step 16 as reference quantities withwhich output signals s1 and s2 of sensors 3 and 5 are compared. Thiscomparison may be a threshold value comparison. If signals s1 and s2match exactly or if they correspond to the reference quantities within acertain tolerance range, then in method step 17 this may be regarded assatisfying a first criterion for deciding that the impact has beencaused by a pedestrian.

[0019] In method step 18, change in velocity Δv of the vehicle caused bythe impact is determined by forming the difference between velocity v ofthe vehicle before impact s1, as measured by sensor 3 on bumper 2, andvelocity v of the vehicle after impact s2, as measured by sensor 5 onengine hood 4. Likewise, the change in acceleration Δb of the vehiclecaused by the impact is determined in method step 19. The change inacceleration Δb is obtained from the difference between the accelerationb measured before impact with the bumper and the acceleration b measuredafter impact with the engine hood. Acceleration b may preferably bedetermined with an acceleration sensor which is also used forcontrolling deployment of the restraint systems in the vehicle.

[0020] In method step 20, the change in velocity Δv thus determined andthe change in acceleration Δb thus determined are each compared with areference quantity. The velocity range in which the safety device forthe pedestrian is to be deployed may be approximately in the range of 15km/h to 55 km/h. The velocity of the vehicle may change by approximately5 km/h in a pedestrian impact, and the acceleration may change byapproximately 3 g (g is the acceleration due to gravity) if there is nobraking before or during the impact, or by approximately 4 g if there isbraking. To take into account the braking operation in determining thereference quantities, brake signal br regarding a braking operation mayalso be taken into account in method step 20.

[0021] If change in velocity Δv and change in acceleration Δb duringimpact match the reference quantities, or if they match them within acertain tolerance range, then in method step 21 a second criterion forthe decision that a pedestrian impact has occurred is considered to besatisfied. The second decision criterion may also be a function ofeither the change in velocity Δv alone or the change in acceleration Δbalone. However, if braking is already performed before impact, then thechange in velocity Δv may not be used to form the second decisioncriterion, because in brake-locked wheels, the measured velocity has avalue of 0 and therefore may no longer be used for determining velocitydifference Δv.

[0022] In method step 22, the two decision criteria determined in steps17 and 21 are subjected to an AND operation, and if both decisioncriteria are met, it is decided in method step 23 that it is apedestrian impact. As a result of this, available pedestrian safetydevices may be deployed.

What is claimed is:
 1. A method of detecting the impact of a pedestrianwith a vehicle; using at least one sensor (3) on the bumper (2) and atleast one sensor (5) in the area of the front edge of the engine hood(4), the pressures or deformations caused by an impact being measured,and a first criterion (17) for the decision as to whether pedestrianimpact has occurred being formed from the sensor output signals (s1, s2)by comparison with reference quantities, wherein the change in velocity(Δv) and/or the change in acceleration (Δb) of the vehicle (1) caused byan impact is determined, a second criterion (21) for the decision as towhether pedestrian impact has occurred is formed, by comparing thechange in velocity (Δv) and/or the change in acceleration (Δb) with areference quantity, and if both decision criteria (17, 21) are met, itis decided that pedestrian impact has occurred.
 2. The method accordingto claim 1, wherein braking (br) initiated before an impact is takeninto account in deriving the second decision criterion (21).
 3. Themethod according to claims 1 and 2, wherein, if braking (br) isinitiated before an impact, the second decision criterion (21) isderived only from the change in acceleration (Δb).
 4. The methodaccording to claim 1, wherein the signal amplitudes of the sensor outputsignals (s1, s2) are compared with reference amplitudes typical of apedestrian impact.
 5. The method according to claim 1, wherein thechronological sequence of the output signals (s1, s2) of the sensors (3,5) on the bumper (2) and in the area of the front edge of the enginehood (4) are compared with a chronological signal sequence (Δt) typicalof a pedestrian impact.
 6. A device for detecting an impact of apedestrian with a vehicle, having at least one sensor (3) on the bumper(2) and at least one sensor (5) in the area of the front edge of theengine hood (4) to measure the pressures or deformations caused by animpact, and having means (6) which compare the sensor output signals(s1, s2) with reference quantities to derive a first criterion (17) forthe decision as to whether a pedestrian impact has occurred, whereinmeans (7, 8) for detecting changes in velocity and/or accelerationcaused by an impact are provided; means (6) are provided for deriving asecond criterion (21) for the decision as to whether pedestrian impacthas occurred, by comparing the changes in velocity and/or accelerationto a reference quantity, and means (6) are provided to decide thatpedestrian impact has occurred if both decision criteria (17, 21) aremet.
 7. The device according to claim 6, wherein the sensors (3, 5) arewire strain gauges.
 8. Device according to claim 6, wherein the sensors(3, 5) are made of piezoelectric films.
 9. The device according to claim6, wherein the sensors (3, 5) are based on the anisotropicmagnetoresistive effect.
 10. The device according to claim 6, whereinthe sensors (3, 5) are based on the Hall effect.
 11. The deviceaccording to claim 6, wherein the sensors (3, 5) are made up of elementshaving pressure-dependent light-transmission characteristics.